docs(tank): add concept images to README and docs site

Add WIP notices to README and docs index. Add all 9 concept mockup
images (idle, overlay, tool-exec, multi-pane, multi-agent, command
palette, services, services-logs, detach/reattach). Create dedicated
concepts.md page. Add GitHub Pages deployment workflow.

Author: jhhuh

.github/workflows/docs.yml

@@ -0,0 +1,42 @@
+name: Deploy docs
+
+on:
+  push:
+    branches: [master]
+    paths:
+      - 'docs-site/**'
+      - '.github/workflows/docs.yml'
+  workflow_dispatch:
+
+permissions:
+  contents: read
+  pages: write
+  id-token: write
+
+concurrency:
+  group: pages
+  cancel-in-progress: true
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-python@v5
+        with:
+          python-version: '3.12'
+      - run: pip install mkdocs-material
+      - run: mkdocs build -f docs-site/mkdocs.yml -d ../site
+      - uses: actions/upload-pages-artifact@v3
+        with:
+          path: site
+
+  deploy:
+    needs: build
+    runs-on: ubuntu-latest
+    environment:
+      name: github-pages
+      url: ${{ steps.deployment.outputs.page_url }}
+    steps:
+      - id: deployment
+        uses: actions/deploy-pages@v4

README.md

@@ -1,11 +1,61 @@
 # Tank
 
+> **Work in progress** — Tank is in early development. The protocol and
+> architecture are being designed; the Haskell implementation covers core CRDT
+> types, a VT100 emulator, standalone terminal mode, and a daemon skeleton.
+> APIs, commands, and interfaces will change.
+
 A protocol-centric workspace system with terminal multiplexing, per-pane
 coding agents, and seamless session migration.
 
 Named after Tank from The Matrix — the operator who loads programs, monitors
 the crew, and runs the console.
 
+## Concept
+
+<!-- concept images generated by docs-site/docs/assets/concepts/render-concepts.py -->
+
+### Idle terminal
+
+![Idle terminal](docs-site/docs/assets/concepts/01-idle.png)
+
+### Per-pane coding agent (operator)
+
+![Agent overlay](docs-site/docs/assets/concepts/02-overlay.png)
+
+The operator reads files, executes commands, and writes fixes — all inside the
+overlay:
+
+![Agent tool execution](docs-site/docs/assets/concepts/03-tool-exec.png)
+
+### Multi-pane layout
+
+![Multi-pane split](docs-site/docs/assets/concepts/04-multi-pane.png)
+
+Each pane gets its own independent operator:
+
+![Multi-pane agents](docs-site/docs/assets/concepts/05-multi-agent.png)
+
+### Command palette
+
+![Command palette](docs-site/docs/assets/concepts/06-windows.png)
+
+### Per-project services
+
+Manage project daemons via Procfile:
+
+![Services overlay](docs-site/docs/assets/concepts/07-services.png)
+
+Live daemon logs with tree view:
+
+![Services logs](docs-site/docs/assets/concepts/08-services-logs.png)
+
+### Session persistence
+
+Detach and reattach — sessions survive disconnects:
+
+![Detach and reattach](docs-site/docs/assets/concepts/09-detach.png)
+
 ## Features (MVP)
 
 - Terminal multiplexer with pane splits and sessions
@@ -60,7 +110,11 @@ devshell managers) are **plugs** that communicate via a Cap'n Proto binary
 protocol. State is synchronized using CRDTs with an epoch-tagged LWW grid and
 spatial jitter buffer for terminal screen sync.
 
-See [Protocol Design](docs-site/docs/protocol.md) and [Architecture](docs-site/docs/architecture.md) for details.
+See the [documentation site](docs-site/docs/index.md) for details:
+
+- [Architecture](docs-site/docs/architecture.md)
+- [Protocol Design](docs-site/docs/protocol.md)
+- [Terminal Screen Sync](docs-site/docs/screen-sync.md)
 
 ## Origin